FRIDAY, June 19 (HealthDay News) -- The most commonly used test to measure intelligence is underestimating the intellectual potential of autistic people, new research suggests.

People with autism often struggle with the verbal portions of the Wechsler Adult Intelligence Scale, the test most often used to measure IQ, researchers said.

But when given another test of abstract reasoning abilities, the Raven's Standard Progressive Matrices, autistic people not only had scores equal to those of their non-autistic counterparts, but they answered the questions, on average, as much as 42 percent more quickly.

On the Raven's test, autistic participants scored, on average, 30 percentage points higher than would have been predicted by their scores on the Wechsler scale, according to the study, in the June issue of Human Brain Mapping.

Also, MRIs done during the testing showed that autistic people had more activity in different areas of their brains than those without autism.

"While both groups performed Raven's Standard Progressive Matrices (RSPM) test with equal accuracy, the autistic group responded more quickly and appeared to use perceptual regions of the brain to accelerate problem solving," said Isabelle Soulieres, a post-doctoral fellow at Harvard University and the study's lead author. "Some critics argued that autistics would be unable to complete the RSPM because of its complexity, yet our study shows autistics complete it as efficiently and have a more highly developed perception than non-autistics."

The researchers said the findings have implications for the way in which autistic children are educated.

"When we do the Wechsler test, which is the one that is done in clinical settings, there is a big chance that we underestimate the education potential of autistics," Soulieres said. "If you underestimate someone's potential, you will have less hope and you will lower your goals for this person. We should make the bet they are more intelligent than they show us on the Wechsler test."

For the study, 15 autistic people ages 14 to 36 were matched with 18 people without autism. Based on their preliminary results on the Wechsler test, all participants had an IQ between 81 and 131, or generally between the low and high end of the normal range.

Each participant was then given the Raven's Standard Progressive Matrices, a 60-item test of abstract reasoning ability. The questions, which are highly visual in nature, ask participants to identify the next sequence of a larger pattern or the missing segment of complex geometric shapes.

During the test, MRIs indicated that people with autism showed more activity in the left cuneus, a region of the brain's occipital cortex thought to be involved with updating working memory and making comparisons among visual images, according to the study.

Compared with people without autism, autistic people showed less activity in areas of the prefrontal cortex of the brain that are thought to be involved in manipulation and integration of information in working memory, managing difficult tasks and evaluating the correctness of responses.

When it came to their answers, those with and without autism who scored the same on the Wechsler test also had similar scores on the Raven's test. But those with autism answered figural questions 23 percent more quickly and analytic questions 42 percent more quickly.

"This study bolsters our previous findings and should help educators capitalize on the intellectual abilities of autistics," said senior researcher Dr. Laurent Mottron, a professor of psychiatry at the University of Montreal. "The limits of autistics should constantly be pushed, and their educational materials should never be simplified."

Autism is marked by repetitive behaviors, problems with verbal or non-verbal communication and social difficulties. Because the condition has a wide range of symptoms and degrees of severity, autism is now often referred to as autism spectrum disorders, said Brenda Smith Myles, chief of programs for the Autism Society of America.

Previously, many experts believed that as many as 70 percent of people with autism also had cognitive and other learning disabilities. But recently, researchers have been finding that perhaps only half do, Myles said.

Studies such as this one show that people with autism are able to problem solve and that visual learning might be more helpful than auditory or language-based learning.

Still, she said, there's a need for more studies to assess how best to put such knowledge into practice in the real world to help autistic people succeed in school and employment.

"What we need are more studies that take this information and apply it in a classroom or community setting," Myles said. "This does not tell us what a child will do in a third-grade classroom or what an adult will do in a workplace."